The molecular underpinnings for specifying neuronal diversity and decline largely remain a mystery. One emerging idea is that the mobilization of transposons during aging and disease can disrupt the normal transcriptome profiles of individual neurons and alter animal activity. In both Drosophila and humans, the dominant transposon classes are retrotransposons which primarily mobilize via an RNA intermediate. Since RNA surveillance pathways, such as the RNAi-small RNA and Adar-RNA editing pathways, are key mechanisms implicated in transposon regulation, we hypothesize they also mediate neuronal diversity during development, but may decline during aging. To test this hypothesis, we will achieve the following aims in this project: Aim 1: Discover changing Transposon Landscapes (TLs) in Drosophila aging brains and neurons. Aim 2: Discover transcriptome and RNA editing changes in aged Drosophila brains and neurons that can be linked to changing TLs. Aim 3: Assess TLs and transcriptomes in brains with modulated RNA surveillance pathways. We will deeply sequence the genomes and transcriptomes from brains and highly purified neurons that regulate Drosophila activity. These data will allow us to integrate TL dynamics along with the diversification of RNA repertoires. Importantly, we will go beyond simple quantitative changes of coding mRNAs, because we will also discover novel RNA- editing events, lncRNAs, and small RNA populations. These transcriptome alterations may all converge on transposon regulation, so we will also examine if genetic modulation of RNAi/small RNA and Adar/RNA editing pathways can help neurons manage changing TLs and promote greater longevity and activity in aging animals.